Power-amplifier control circuits are used to regulate the output power of an amplifier, such as those used in mobile phones. These amplifiers can be subject to extreme operating conditions, such as a widely varying power supply voltage. A closed-loop feedback controller, that senses the output power and compares it with a reference, is typically added to a power amplifier to stabilize its output level. In this arrangement an input amplifier is used at the input as interface for the input control voltage. The input amplifier conditions the internal reference voltage for the error or loop amplifier in terms of voltage level, polarity and gain. The input amplifier and the power-amplifier usually share the same single voltage supply.
In the prior art, the input amplifier has been implemented using low input rail amplifier topology. However, in a standard, low input rail amplifier topology, power supply leakage can occur in the differential-to-single-ended conversion stage at the output of the input amplifier. There is a need, therefore, to improve power supply rejection to maintain a stable reference voltage, and thereby achieve near supply voltage independent, accurate power regulation.